Bouyancy

using UnityEngine;
using System.Collections;

public class Bouyancy : MonoBehaviour {

    public float offset;
    public float mass;
    public float density;
    float waterHeight;
    public float gravity;
    public float fluidDensity;
    public float dampingCoefficient;
    Vector3 boatSize;
    public float percentUnderwater;

    float yVel;

    // Use this for initialization
    void Start () {
        Ray ray = new Ray(transform.position + new Vector3(0, 500, 0), Vector3.down);
        RaycastHit[] hits = Physics.RaycastAll(ray);
        foreach (RaycastHit hit in hits){
            if (hit.transform.gameObject.layer == 4){
                waterHeight = hit.point.y;
            }
        }

        BoxCollider boxcol = this.gameObject.GetComponent("BoxCollider") as BoxCollider;
        boatSize = boxcol.size;
    }

    // Update is called once per frame
    void FixedUpdate () {

        percentUnderwater = (waterHeight - (transform.position.y - offset - (0.5f * boatSize.y)))/boatSize.y;
        if (percentUnderwater < 0f) percentUnderwater = 0f;

        float accelY = 0f;
        accelY = gravity * (fluidDensity/density * percentUnderwater - 1f);
        yVel += (accelY);
        yVel *= dampingCoefficient;

        transform.position += new Vector3(0f, yVel, 0f);
    }
}